Control of insects and microorganisms are of most importance for improving storage period of stored products.
The main antimicrobial preservation technologies used to preserve the overall quality of the food over certain duration, known as the shelf life are thermal processing, chilling and freezing, concentration, drying, ionizing radiation, chemical preservation, high hydrostatic pressure, pulsed electric field, and intense light.
Regarding the protection against insects physical, biotechnical, biological and chemical methods are involved.
The physical control is the manipulation of the physical environment so that insect populations do not increase or are reduced and eliminated. The physical attributes refer to temperature, relative humidity, moisture content, structures containing the commodity (silos, elevators, bags, packaging), forces on commodity (compression, impaction), inert dusts (diatomaceous earth), irradiation and packaging. Inert dusts control insects by damaging the cuticle and causing the insects to desiccate. Inert dusts are used to a limited extent commercially.
The main problems with the use of inert dusts are that they decrease the bulk density and flow ability of grain, are dusty to apply, and are ineffective in some cases. Gases are also a component of the physical environment. The main advantages are that they are not toxic to mammals and provide continued protection from insects. The hermetic storage of grain is one form of modified atmospheres by which grain itself through respiration creates an atmosphere rich in carbon dioxide and low oxygen. The atmospheres are modified to attain low oxygen environments by adding carbon dioxide, nitrogen, or burning the storage facility atmosphere and recirculating the combustion products. The term “controlled atmosphere” usually refers to the process of changing the atmosphere of a facility artificially by introducing CO2 or N2. In changing the atmosphere of a storage facility, we expect to create an environment that will not support insects or mycoflora in the storage facility.
The disadvantages of using modified atmospheres for insect control are the length of time required to obtain control as well as the cost of application and getting an adequate supply of gas to the treatment site. CO2 can cause flavour deterioration.
Ambient air cooling is used mainly for control of insects in bulk grain storage. However, it has been also used in controlling insects in flour mills as an alternative to fumigation. Modified atmospheres have many advantages. They provide a way to eliminate insects from stored commodities without polluting the atmosphere and are safer than fumigants.
The biotechnical methods are related to traps with pheromones and traps with food baits which are not directly related to the object of present disclosure.
The biological control employs parasites, predators, or pathogens, microorganisms that cause disease and are distinguished by the fact that they are capable of reproducing after release, to suppress pest populations. It is important to understand that biological control can only be used as a prophylactic, not remedial, strategy, and that it will be most effective when integrated with other control strategies such as sanitation, fumigation, aeration, and packaging.
All insect pest populations tend to increase exponentially as long as there is adequate food, suitable environment, and no predators or parasites. Pest control has focused on the use of pesticides, exclusion (packaging), and adverse environmental conditions (desiccation, modified atmosphere, or temperatures extremes) to suppress stored product insects.
Most stored-product insect pests are probably not suitable for classic biological control, because their natural enemies have been distributed as widely as the pests.
The application of microbial agents for biological control of stored product pests is similar in technique and philosophy of use to the application of chemical protectants.
Further reductions of chemical control can be achieved by substituting biological and physical for chemical control methods. Decreased reliance on chemical control methods is the best resistance management program. Synthetic chemicals must be used to a lesser degree because of the concern about chemical residues on grain, worker safety, the environment, and insecticide-resistant populations. Extreme temperatures are currently the most widely used physical control method. Insects cannot grow and reproduce below 13° C. or above 35° C.
The main method by which storage fungi can be controlled is through drying and cooling. Chemical treatment to prevent fungal growth can only be used on grain for animal feed (FAO-www.fao.org/docrep/x5036e/x5036eOp.htm, site accessed at 24 Aug. 2015).
Modified atmospheres containing high CO2 levels could also be employed and that O2 should preferably be completely excluded for the protection of maize from fungal spoilage and mycotoxin contamination during the post-harvest period.
Gamma irradiation can be used to prevent the growth of aflatoxigenic fungi and to reduce the AFB1 levels in various goods intended for animal and human consumption, thus minimizing the animal and human exposure to this carcinogenic mycotoxin.
However, in low to medium scale of production mainly in developing countries synthetic fungicides are still used to control stored grains pests. The indiscriminate use of synthetic antifungals has led to the development of resistant strains which has necessitated utilization of higher concentrations, with the consequent increase in toxic residues in food products.
The salts of weak acids, such as sodium benzoate and potassium sorbate, can inhibit growth of several postharvest fungal pathogens. Using these compounds for fungal inhibition presents several benefits, such as their low mammalian toxicity, a wide spectrum of activity and relatively low cost. However, high concentrations of these compounds are needed to act as fungicides, bringing associated potential organoleptic changes [Lucía da Cruz Cabral, Virginia Fernández Pinto, Andrea Patriarca (2013). Application of plant derived compounds to control fungal spoilage and mycotoxin production in foods. International Journal of Food Microbiology, 166:1-14].
The indiscriminate and excessive use of fungicides in crops has been a major cause of the development of resistant pathogen populations, resulting in the use of higher concentrations of these antifungals and the consequent increase in toxic residues in food products. Some of these compounds are not biodegradable, so they can accumulate in soil, plants and water, and consequently affect humans through the food chain. Although chemical treatments have been considered to be the cheapest and most effective way to prevent postharvest diseases, the development of resistant microorganisms has reduced their acceptance. The type and concentration of fungicides allowed for postharvest application are restricted due to their long degradation period and potential effects on food and human health (carcinogenicity, teratogenicity, high and acute residual toxicity, hormonal imbalance and spermatotoxicity). Because of these undesirable effects, recent studies resulted in the revocation of registration of some of the more effective fungicides. Furthermore, public concern about food contamination with fungicidal residues has significantly increased. Considering all these factors, the development of new safe and biodegradable alternatives that are both effective and economically feasible is needed [Lucía da Cruz Cabral, Virginia Fernández Pinto, Andrea Patriarca (2013). Application of plant derived compounds to control fungal spoilage and mycotoxin production in foods. International Journal of Food Microbiology, 166:1-14].
Knowledge on biocidal properties of plant essential oils increased their relevance to solve problems of pest control in food stuff and food commodities. There are several reports of the use of essential oils in controlling pests of crops. The essential oils from aromatic plants have antiseptic and biocidal properties, potentially useful for the protection and conservation of foods, in particular applicable in increased shelf life strategies, as known in the prior art. However there are few reports of its use in food preservation, in particular food grain, dried, stored for long periods of storage.
The present disclosure relates to the use of essential oils rich in eugenol and pulegone. More specifically relates to essential oils from Syzygium aromaticum (clove) and Mentha pulegium (pennyroyal). The oils may be obtained by any of the methods known in the art (e.g. hydrodistillation, supercritical extraction). Some reports on the use of essential oils for food products stored are known. For instance the WO 2001000049 A1 and the US 20030091661 A1 describe methods to control pests, mites and beetles respectively, and affecting food stored products by the use of pesticides based on plant essential oils. However in both cases the pesticide is a fumigant applied by contact to foods within the containers or cartons where food products are stored.
This disclosure is not a fumigant and it should not be sprayed for contact action. The document CN102388958 describes a method for grain pest control using essential oils. However, its use in containers is not included. The objective of the present application is to contribute to solve the need for methods to protect stored products from pest thereby preserving the stored products inside closed containers of considerable dimension (over 60 L). Other studies related to repellence of spices are also known, even against S. zeamais; however repellence effects are not considered for the present objective.
The effects of plant oils based on repellence activity to avoid external contaminations in stored packaged foodstuff were also found, when applied only to very small capacity containers, based on a method very different from the present purposed system.
These facts are disclosed in order to illustrate the technical problem addressed by the present disclosure.